As is known in the fertilizer art, carnallite is a valuable compound in view of the fact that it contains potassium chloride, which is valuable to various industries and in particular, to the fertilizer industry. Carnallite is described by the formula KCl—MgCl2-6H2O.
Currently, when potassium chloride ore is mined, it must undergo significant unit operations for upgrading, which is costly and significantly increases the price of this commodity. For example, a typical mine is at least a kilometre deep and is of the shaft variety. Accordingly, this involves a tremendous amount of expenditure in teens of the drilling of the shaft and additionally involves specialized tunnelling to accommodate work areas. Generally speaking, tunnels in these types of mines can exceed six kilometres in length and take inordinate amounts of time to drill. Once mined, the material must then be crushed, ground and deslimed as initial unit operations. Typically, this source of potassium chloride is affected by unacceptably high levels of salt (sodium chloride) contamination, which makes it un-saleable.
In order to diminish the quantity of sodium chloride present, the mined product must undergo flotation to remove the excessive sodium chloride. Once this is done, the product must then be dried and sized with further processing in terms of compaction and crystallization. One of the problems with the latter stages of processing is the storage aspect. Storing the potassium chloride for lengthy periods of time is problematic, since the product is inherently hygroscopic. This results in coagulation and agglomeration of the crystals in to lumps.
Even with the degree of flotation that is typically employed to produce a commercial grade of potassium chloride fertilizer, the existing product in the marketplace is typically impure and has occluded impurities as well as a significant degree of magnesium chloride and sodium chloride contamination.
In order to attempt to circumvent the limitations in conventional potassium chloride production, solution mining has been employed.
Solution mining is a widely known mining engineering technique and has been used extensively to extract evaporite values from subterranean formations for many years.
The intrinsic value of the evaporites is realized in the fact that contained potassium is the progenitor for potash production. The necessity of potash for crop production, animal feed inter alia is well known. The value of potash has increased and now approximates that of crude oil. The escalating price of potash is based on unprecedented pressure currently experienced by farmers for greater and greater food production. Demand has increased prices.
In U.S. Pat. No. 3,644,102, issued Feb. 22, 1972, Svanoe teaches a crystallization process of potassium chloride from the decomposition of carnallite. The process involves the use of potassium chloride crystals as seeding agents in a solution of carnallite and potassium chloride with crystallization of the crystals followed by separation from the initial mother liquor.
There is no provision in the teachings for preventing sodium chloride contamination.
Sadan, in U.S. Pat. No. 4,140,747, issued Feb. 20, 1979, provides a process for the production of potassium chloride and of magnesium chloride hexahydrate (bischoffite) from carnallite or from carnallite containing sodium chloride. In the process, carnallite is heated to a temperature of between above 70° C. and above 167.5° C. Solid potassium chloride is then separated. In the residual brine, carnallite is precipitated by evaporation or by lowering the temperature, and it is recycled to the starting stage. The residual solution consists essentially of magnesium chloride which is recovered as bischoffite.
Similar to the Svanoe document, the Sadan teachings do not specifically provide instruction for preventing significant sodium chloride contamination.
A process for the treatment of carnallitic ores is discussed in U.S. Pat. No. 4,504,092, issued Mar. 12, 1985, to Bichara et al. Carnallitic ores are treated with a decomposition-brine containing amounts of magnesium chloride, potassium choride chloride and sodium chloride for precipitating artificial sylvinite in a solution of magnesium chloride saturated in potassium chloride and NaCl. The invention relates to the addition to the decomposition-brine of a collector for the flotation of KCl and a source of gas, so as to contact newly formed crystal nuclei of KCl selectively with the collector and to contact bubbles of gas with the collector. This forms a froth enriched in KCl simultaneously with the decomposition of carnallite.
A technique for the purification of crystalline potassium chloride is set forth in U.S. Pat. No. 4,385,902, issued May 31, 1983 to Haugrud.
The method comprises leaching under isothermal conditions compacted particles of a particle size from 8 to 200 Tyler mesh of potassium chloride with an aqueous leaching solution. The solute of the solution is selected from potassium chloride and mixtures of potassium chloride and sodium chloride. The leaching solution is saturated with respect to potassium chloride and contains less than 45 grams of sodium chloride per litre of solution, for a time sufficient to reduce the sodium chloride content of the compacted particles and separating leached particulate potassium chloride product having a sodium chloride content of less than about 0.5 weight percent from the leaching solution.
In light of the foregoing, production has increased absent concomitant improvements in the existing solution mining techniques.
The techniques for solution mining currently followed involve the formation of a cavern into which water is injected as a solvent. This in and of itself is fine, however, volume control of the cavern is often uncontrolled and this results, depending on tectonics, in eventual subsidence of the formation. This is exacerbated by the fact that the formation pressure is not maintained during growth of the cavern. Accordingly, the mine is productive though with environmental consequences.
Perhaps one of the most significant limitations with existing techniques is the issue concerning tailings. By present methods, the tailings can be significant, require special handling and occupy large areas for storage.
It would be desirable to realize the benefits of solution mining in a carnallite deposit also having sylvinite contained therein without the limitations of existing methodology.
As is demonstrative of the existing limitations of the art, current process engineering of the potassium chloride results in a product that is at best 95% pure potassium chloride.
The present invention satiates the need for such a combination not only in the oil and gas industry, but also other industries where actuator driven arrangements are widespread.